The vestibular system serves to maintain orientational, postural, and visual stability during head movements. The vestibulo ocular reflex (VOR) is an important vestibular mechanism that rotates the eyes to maintain binocular fixation on a target during head movement, thus maintaining clear and stable vision. The VOR is actually a set of reflexes activated by two forms of head acceleration; angular (the AVOR), driven by the semicircular canals, or linear (the LVOR), driven by the otoliths. The otolith organs sense linear accelerations caused by both head translation and head tilt relative to gravity, yet each form of motion requires different compensatory responses. Thus, the LVOR is comprised of both translational and tilt forms. The vestibular system may undergo functional changes in response to development, aging, or disease processes, but is able to modify its behavior such that binocular fixation is maintained during head movements. This process, known as adaptive plasticity, is well recognized in the AVOR, but is largely unstudied in the LVOR. We will study adaptive plasticity of the AVOR and translational LVOR in response to novel visual/vestibular challenges. The resulting behavior of these challenges on the AVOR and LVOR will be assessed and compared. This research will elucidate the extent to which the AVOR, translational LVOR, and tilt LVOR, are driven by shared neural pathways, or if control of each subsystem is independent. Selective adaptation of the VOR will be exploited to formulate structural and functional characteristics of central VOR pathways, and suggest stages of neuronal processing where adaptation may occur. In addition, VOR and motion perception mechanisms share common sensory inputs, as well as the common goal of maintaining spatial orientation. To determine if VOR and motion perception share common pathways, the effects of AVOR and translational LVOR adaptation on the perception of motion and tilt will also be examined. The study of LVOR adaptation will directly contribute to our understanding of how the vestibular system adapts to natural development, disease and aging processes, and to the unnatural gravitational environments encountered during air and space travel. A better understanding of LVOR adaptation will catalyze tests of susceptibility to motion sickness (including the form experienced in space flight), and countermeasures to prevent or reduce this syndrome.